The application of polymeric composite membranes can be very interesting in the field of gas separation. The two main parameters which determine the applicability of membranes are the selectivity and the permeability. Good selectivities can be achieved by developing proper materials, high permeation rates can be obtained by minimizing the thickness of the separation layer. Special attention is paid so far for glassy polymers which generally show higher selectivities than rubbery polymers. However, caused by the often rigid structure of the glassy polymers, defects in the these layers can occur which have a dramatic influence on the selectivity. The objective of this thesis is to investigate, which parameters may influence the preparation of composite membranes. The membranes were coated by the dipcoating method. Polycarbonate (Makrolon 3200) and poly(methyl methacrylate) (PMMA) were used as coating polymers. Three commercial polyacrylonitrile ultrafiltration membranes (GFT, Stork 3010, Stork 5010) were used as support materials.